Mayor de Blasio, flanked by his wife and two teenage kids, used his formal inauguration to promise that New York will become a different city — “a fairer, more just, more progressive place” after 12 years of the Bloomberg administration.

On a frigid day outside City Hall, de Blasio served notice Wednesday that he will use his November election landslide as a liberal mandate for sweeping and immediate change.

“We won’t wait. We’ll do it now,” he repeatedly vowed to a cheering audience of 5,000 that included the city’s most prominent Democrats.

The 109th mayor echoed his campaign themes and promises, using the word “progressive” seven times during his speech.

“When I said we would take dead aim at the tale of two cities, I meant it. And we will do it,” he said. “I will honor the faith and trust you have placed in me. And we will give life to the hope of so many in our city. We will succeed . . . as one city.”

The most unabashedly left-leaning mayor in memory even invoked the “1 Percent,” the wealthy who were demonized in the rhetoric of the Occupy Wall Street protests.

“We will require big developers to build more affordable housing. We’ll fight to stem the tide of hospital closures,” de Blasio said.

Bill De Blasio (right) is sworn in as NYC’s 109th mayor by President Bill ClintonSteve Sands/WireImage

“And we’ll expand community health centers into neighborhoods in need, so that New Yorkers see our city not as the exclusive domain of the 1 Percent, but a place where everyday people can afford to live, work and raise a family,” he added. “We won’t wait. We’ll do it now.”

The speech drew effusive praise, including from former President Bill Clinton, who administered de Blasio’s oath of office, with a Bible once used by President Franklin D. Roosevelt.

“I thought it was completely consistent with his campaign,” Clinton said. “It was very positive, embracing, inclusive. I liked it.”

Former Mayor Bloomberg attended and sat stone-faced as several speakers, including new Public Advocate Letitia James, vilified his administration.

The Rev. Fred Lucas of Brooklyn, who gave one of four invocations, shockingly referred to “the plantation called New York City” in his remarks. Most of the speakers, who were led off by singer Harry Belafonte, repeated the mayor’s call to end ”inequality.”

De Blasio didn’t take part in the Bloomberg bashing and struck some middle-of-the-road themes. When he said, “We recognize a city government’s first duties,” he immediately followed with “to keep our neighborhoods safe.”

And when he vowed to “reform a broken stop-and-frisk policy,” he said this was intended “both to protect the dignity and rights of young men of color” but also “to give our brave police officers the partnership they need to continue in their success in driving down crime.”

(From left) Former Mayor Michael Bloomberg, Sandra Lee, Gov. Andrew Cuomo, Bill and Hillary Clinton attend the inauguration ceremony of Bill de Blasio on the steps of City Hall.Steve Sands/WireImage

And the role of families in general — and his in particular — was a recurring theme of the speech. After thanking the VIPs attending, he praised his wife — “Chirlane, you are my soulmate — and my best friend. My partner in all I do.”

“Chiara and Dante,” he added, to his children, “I cannot put into words the joy and the pride that you bring your mother and me.”

Clinton had introduced de Blasio, saying he represents, with his family, “the future of our city and our country.”

“They are our real ‘Modern Family,’ ” he said, to laughter and applause.

The family theme struck a chord with many in the audience.

“I just love when he talks about his family, because he’s so good and he always gives credit,” said Linda Brandel, 67, of Windsor Terrace, Brooklyn, a volunteer in de Blasio’s campaign. She wore a necklace she made with tokens that had head shots of each de Blasio family member pasted on.

“We’ve got the right man and the right family, and I’m proud to be an American again.”

There was no mistaking the new mayor’s agenda. He devoted a sizable portion of his inaugural address to a pitch for taxing the wealthy to fund full-day pre-K and after-school programs.

“Those earning between $500,000 and $1 million a year, for instance, would see their taxes increase by an average of $973 a year,” he said.

“That’s less than three bucks a day — about the cost of a small soy latte at your local Starbucks,” he added to applause and laughter.

De Blasio had been officially sworn in one minute after midnight in a ceremony at his Brooklyn home. Those who managed to get to the more public festivities 12 hours later at City Hall said they weren’t disappointed.

“It’s what I expected the new mayor to say, and I think it resonated with I would say the majority of the city,” said Kevin O’Keefe, 53, a digital product designer from Murray Hill.

“The tale of two cities — I know we’ve heard it before, but to me that’s what stuck out the most,” said O’Keefe, who came with his wife and three children.

After the speech, de Blasio retired to City Hall, where he shook hands with a line of 1,300 well-wishers for more than three hours.